An automatic testing machine (ATM) operates in a production environment to rapidly and accurately test the operation and performance of various types of devices under test (DUT), including computer devices and communication devices. The DUTs could be a finished product or a component of a larger system.
The ATM is programmed to perform various tests on the DUT automatically. For example, a microcomputer chip DUT may be fed power and known input signals, and the output signal of the DUT is compared with expected results. Another example is where RF signals are transmitted to a finished cellular telephone DUT to determine if the telephone properly operates. Other tests could include environmental tests, such as temperature tests.
Depending upon the nature and number of the tests being performed, the testing may last from a couple of milliseconds to several minutes. The information from the testing is compared with expected test results. If there is some defect such that the DUT falls below specifications, the ATM will designate the DUT as failed, either by marking the DUT, placing the DUT in a failure area, or indicating the failure to an operator.
The ATM is then loaded with the next DUT, either manually or automatically, and the testing procedure is repeated for this next DUT. This testing information can be used to evaluate the fabrication process for possible changes, as well as to perform failure analysis on individual failed devices.
Typically, each ATM is designed to perform a specific class of tests on the DUT, and are not able to perform other classes of tests. For example, a temperature ATM may not be able to perform electrical signal tests. However, different types of DUTs may require the same tests to be performed. For example, all types of microcomputer chips are tested for electronic performance characteristics, but different chips will have different locations for power, inputs and outputs. ATMs are made flexible by the use of test fixtures. The test fixture provides an interface between the device under test DUT and the ATM. Thus, a single ATM can perform tests on different types of devices when connected via different fixtures.
The automatic testing machines generate a great deal of vibration. The sources of the vibration include the operation of robots to load and unload the DUTs, operation of the testing machines, manipulation of the DUTs during testing, and the tests themselves, i.e. sound tests. These vibrations are passed on to the DUT and can adversely effect the testing of the DUT. Some types of testing, particularly acoustic testing, are very sensitive to vibration energy or sound energy, especially low frequency energy. The testing of the DUT may be corrupted by the vibrations, which will cause incorrect information about DUT to be collected. The incorrect information could lead to improperly passing a defective DUT or failing a passing DUT. The incorrect information may also result in incorrect or unnecessary changes being made to the DUT production process.
One solution to this problem is to isolate the fixture from the automatic testing machine. A vibrational isolation mechanism is used to separate the fixture from the machine. A variety of such mechanisms are available, for example a pneumatic air table, a spring mechanism, or a foam or rubber isolation pad. Thus, the fixture is not ridgedly attached to the machine. Therefore vibration and/or sound energy from the testing machine, other equipment, or the floor would not be transmitted to the fixture. However, because the fixture is not ridgedly attached to the testing machine, the robots used to load and unload the machine, as well as actuators in the machine which secure the DUT and couple to the DUT, do not know the precise location of the fixture, and hence the DUT. Consequently, the testing machine must use an adaptive mechanism to locate the fixture, and properly place, remove or otherwise manipulate the DUT. The adaptive mechanism could be touch sensors mounted on the robot, or a vision system with an optical object recognition program. Mechanical limits are sometimes used to confine the fixture to a predefined region, i.e. pins or stops. Thus, the fixture can more easily be located by the robot. However, if the fixture touches the limit, then vibration and sound energy will be conducted through the limit and into the fixture. Moreover, the time spent locating the fixture and the DUT adversely affects production time. In other words, it costs production time for the testing machine to have locate the fixture.
Alternatively, the fixture can be ridgily attached to the testing machine. Since the fixture does not move with respect to the testing machine, then the testing machine will always know precisely where the fixture and the DUT are located. Thus additional mechanism such as touch sensors and vision camera are not needed. Moreover, no production time is lost in having the testing machine locate the fixture or device. However, the fixture will receive vibrational and/or sound energy from the testing machine. Thus, vibrations from robot motion, testing structures moving around, conveyor belts, other equipment operating, the floor, etc. will be conducted to the fixture. Thus, the vibrations and other sounds reaching the fixture can corrupt the testing of the DUT, particularly acoustic testing.
Therefore, there is a need in the art for a mechanism that will isolate the fixture from the automatic testing machine, while having the fixture be precisely located such that the testing machine does not require any adaptive mechanism to locate the fixture which would impact production time.